Is that actual superpower plot armor?
No. For Superman, his true superpower is his unshakable moral center, which he acquired from Ma and Pa Kent. He will always do the right thing, for the right reason, at the right time, whatever the cost he must personally pay to do it. As Batman says in a famous comic page, "It is a remarkable dichotomy. In many ways, Clark is the most human of us all. Then...he shoots fire from the skies, and it's difficult not to think of him as a god. And how fortunate we are that it does not occur to
him." (Emphasis in original) His Kryptonian biology is simply an enabler; it
allows his true superpower to display itself, in all its glory.
Batman's superpower is his absolute, unshakable iron will, his
determination. Unlike Superman, he is not a moral paragon; he does have high standards, but he is willing to bend
some rules, even as he upholds others to the end. He's a heroic Magnificent Bastard, who
will uphold his oath. As his DCAU incarnation said to Doctor Destiny, when the latter taunted him psychically:
DD: "We're like
insects to them. They step on us, ruin our lives, and they don't even realize it! But you're different. You don't have any special powers."
Batman: "Oh, I have
one, Johnny:
I never give up."
Each, in his own way, proves the truth of John Dryden's verse: "How ill my fear they by my mercy scan,/Beware the fury of a patient man."